Mercury Vapour Lamp
Definition
A gas-discharge lamp producing discrete atomic emission lines, most useful at 253.7 nm (UV-C germicidal) and 365 nm (UV-A); the classic biological-fluid screening source.
- Light type
- Gas-discharge, discrete emission lines
- Key wavelength
- 253.7 nm (UV-C germicidal)
- Also useful at
- 365 nm (UV-A)
- Common use
- Biological-fluid screening
Common questions
Why is 365 nm specifically useful for screening biological fluids at a scene?+
Many biological fluids, including semen, urine, and some fibers, fluoresce under UV-A around 365 nm, making stains visible on fabric or surfaces that appear unremarkable under normal light. This makes it a standard wavelength for preliminary alternate light source screening.
Is a mercury vapour lamp still the standard choice for scene examination today?+
It has been largely superseded in field kits by tunable LED-based alternate light sources, which are more portable, safer, and can select specific wavelengths on demand, though mercury vapour lamps remain a reference standard because of their well-characterized discrete emission lines.
Related terms
- Alternate Light Source (ALS)
- A device emitting light at selected wavelengths (typically 415 to 535 nm) used to detect biological fluids that fluoresce or absorb light...
- Bandpass Filter
- An optical filter transmitting a defined wavelength range (typically 20-40 nm FWHM) while blocking all others; the excitation filter in an ALS...
- Crime-Lite
- A compact, battery-powered alternate light source system (Foster+Freeman) designed for scene use by scenes-of-crime officers; the Crime-lite 82S and ML2 are standard...
- DFO (1,8-Diazafluoren-9-One)
- A fluorescent ninhydrin analogue used for latent fingerprint development on porous surfaces; excite at 450-470 nm (with secondary absorption extending into the...
- Fluorescent Whitening Agent (FWA)
- An optical brightener added to synthetic fibres and paper during manufacture; fluoresces under UV-A excitation, making treated fibres and paper highly visible...
- Long-Pass (Viewing) Filter
- An optical filter transmitting all wavelengths above a defined cut-on wavelength; worn as goggles by the examiner to block excitation light while...
- Polilight
- Rofin / Omnichrome xenon-arc-based ALS platform developed in Australia; the reference platform for biological-fluid and fingerprint ALS validation studies in Australasian and...
- Rhodamine 6G
- A fluorescent dye applied as a post-treatment to cyanoacrylate-developed fingerprints; excited at 530 nm (green), it emits at 565-590 nm (yellow-orange), greatly...
- Stokes Shift
- The wavelength difference between the excitation peak and the emission peak of a fluorophore. A positive Stokes shift (emission at longer wavelength...
- Tungsten-Halogen Lamp
- A broadband (thermal) light source with continuous emission from UV-A through NIR, determined by filament temperature; the first generation of forensic ALS...
- Xenon Arc Lamp
- A high-pressure xenon discharge lamp producing near-continuous white-light emission across 200-2500 nm; used in broadband ALS platforms (Polilight, CrimeScope) with bandpass filters.